Strong Earthquake strikes Japan; fire at nuclear reactor.

TOKYO (AP) -- A strong earthquake jolted northwestern Japan on Monday morning, flattening dozens of wooden houses, and triggering small tsunamis. Media reports said at least 150 people were injured.

National broadcaster NHK showed footage of the collapsed homes along with damaged bridges and roads. Sirens from fire engines could be heard in hard-hit Kashiwazaki city where the homes collapsed.

Flames and black smoke were seen pouring from the Kashiwazaki nuclear plant, which was automatically shut down in the quake. NHK reported the fire was in an electrical transformer, and that no radioactivity had been released.

Several smaller aftershocks also jolted the region.

"There was a sharp, horizontal shaking lasting dozens of seconds," Hiroki Takahashi, an employee at a gas station in Kashiwazaki, told national broadcaster NHK. "I could hardly stand up."

NHK said more than 150 people were hurt.

The U.S. Geological Survey said the magnitude of the quake was 6.7. It was centered off the coast of Niigata, 160 miles northwest of Tokyo, where buildings swayed during the tremor.

The force of the quake buckled seaside roads and bridges, and one-yard-wide fissures could been seen in the ground along the Niigata coastline.

A ceiling collapsed in a gym in Kashiwazaki where about 200 people were gathered for a badminton tournament, and one person suffered minor facial injuries, Kyodo reported.

A series of aftershocks rattled the area, the largest one with a reported 4.2 magnitude.

Several bullet train services linking Tokyo and northern and northwestern Japan have been suspended, NHK said. NHK said gas services for Kashiwazaki's 35,000 households were suspended after reports of gas leaks.

The Meteorological Agency said small tsunamis as high as 20 inches were believed to have hit coasts in the area. It issued tsunami warnings along the coasts of Niigata but later lifted them. No damage was immediately report.

Prime Minister Shinzo Abe, who was in Nagasaki in southern Japan campaigning for the parliamentary elections later this month, will return to Tokyo to deal with the quake, Kyodo said.

Japan sits atop four tectonic plates and is one of the world's most earthquake-prone countries. The last major quake to hit the capital, Tokyo, killed some 142,000 people in 1923, and experts say the capital has a 90 percent chance of suffering a major quake in the next 50 years.

In October 2004, a magnitude-6.8 earthquake hit Niigata, killing 40 people and damaging more than 6,000 homes. It was the deadliest to hit Japan since 1995, when a magnitude-7.2 quake killed 6,433 people in the western city of Kobe.